Description
The SUM problem can be formulated as follows: given four lists A, B, C, D of integer values, compute how many quadruplet (a, b, c, d ) ∈ A x B x C x D are such that a + b + c + d = 0 . In the following, we assume that all lists have the same size n .
Input
The first line of the input file contains the size of the lists n (this value can be as large as 4000). We then have n lines containing four integer values (with absolute value as large as 228 ) that belong respectively to A, B, C and D .
Output
For each input file, your program has to write the number quadruplets whose sum is zero.
Sample Input
6 -45 22 42 -16 -41 -27 56 30 -36 53 -37 77 -36 30 -75 -46 26 -38 -10 62 -32 -54 -6 45
Sample Output
5
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std ;
int sum1[16000005] ,sum2[16000005] ;
int a[4005] ,b[4005] ,c[4005],d[4005] ;
int n = 0 , t =0 ;
// t = n^2
int Binary_Search(int key)
{
int num = 0 ;
int left = 0 , right = t- 1 ;
while (left <right)
{
int mid = left + (right - left)/2 ;
if(key <=sum2[mid])
right = mid ;
else
left = mid + 1 ;
}
while(sum2[left] == key && left < t )
{
num ++ ;
left ++ ;
}
return num ;
}
int main()
{
int i ;
int j ;
while(scanf("%d",&n)!=EOF)
{
t = 0;
for (i = 0 ;i < n ; i ++)
{
scanf("%d%d%d%d",&a[i],&b[i],&c[i],&d[i]);
}
for (i = 0 ;i<n ;i++)
{
for(j = 0 ; j<n ; j++)
{
sum1[t] = a[i]+ b[j] ;
sum2[t] = c[i] + d[j] ;
t++ ;
}
}
sort(sum1, sum1 + t) ;
sort(sum2 ,sum2 + t) ;
int num = 0 ;
for( i = t-1; i>=0 ;i--)
{
num+=Binary_Search(-sum1[i]);
}
printf("%d\n",num) ;
}
/*
6
-45 22 42 -16
-41 -27 56 30
-36 53 -37 77
-36 30 -75 -46
26 -38 -10 62
-32 -54 -6 45
*/
return 0 ;
}